Light emitting device

ABSTRACT

A light emitting device includes an active layer including atoms A of a matrix semiconductor having a tetrahedral structure, a heteroatom D substituted for the atom A in a lattice site, and a heteroatom Z inserted into an interstitial site positioned closest to the heteroatom D, the heteroatom D having a valence electron number differing by +1 or −1 from that of the atom A, and the heteroatom Z having an electron configuration of a closed shell structure through charge compensation with the heteroatom D, and an n-electrode and a p-electrode adapted to supply a current to the active layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-346601, field Nov. 30, 2005,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitting device based on afilled tetrahedral (FT) semiconductor.

2. Description of the Related Art

In recent years, active research is being conducted on band engineeringfor modulating optical characteristics peculiar to a substance, such asemission and absorption, by modulating the energy band structure thathas been considered to be inherent in the substance.

For example, a quantum dot (or a quantum wire or a superlattice) and astrain effect are well known as a typical band engineering technique.The quantum dot (or the quantum wire or the superlattice) brings about amodulated band structure by reducing the size of a substancethree-dimensionally (or two-dimensionally or one-dimensionally) andconfining electrons therein. The strain effect denotes an effect ofmodulating a band structure by applying a tensile stress or acompression stress to a substance.

On the other hand, a filled tetrahedral (FT) semiconductor istheoretically proposed as a band engineering method for modulating theband structure of a semiconductor in a quite different principle (seeH.W.A.M. Rompa et al., Phys. Rev. Lett., 52, 675 (1984); D. M. Wood etal., Phys. Review B31, 2570 (1985)).

The FT semiconductor is referred to as a solid substance in which a raregas atom or a diatomic molecule with an electron configuration of aclosed shell structure is introduced into the interstitial site of amatrix semiconductor having a tetrahedral structure such as a diamondstructure or a zinc blende structure, as shown in FIG. 1.

A difference in the band structure between ordinary crystal silicon andan FT semiconductor will now be described. FIG. 2A is a band diagram ofcrystalline silicon, and FIG. 2B is a band diagram of silicon doped withHe. FIG. 2B shows the result of the first principle band calculation inrespect of silicon with an FT structure (hereinafter referred to as anFT-silicon), in which a He atom is imaginarily inserted in theinterstitial site of crystalline silicon. As apparent from thesediagrams, the band structure the FT-silicon is modulated into a directtransition type well resembling that of GaAs in which the shape of theconduction band is widely varied from that of the crystalline silicon.One of the effects of the FT semiconductor is that an indirect bandstructure of an indirect semiconductor represented by silicon, that isnon-emissive, is greatly modulated into a direct band structure as toexhibit light-emitting characteristics (or transition probability) of alevel comparable to those of a direct semiconductor such as GaAs.

However, the rare gas-containing FT semiconductor or molecule-containingFT semiconductor proposed by Rompa et al. is believed to be thermallyunstable because the inserted substance can move within the crystal and,thus, not to be suitable for practical use.

Concerning the FT semiconductor, the result of an experiment is reportedthat, if rare gas atoms are ion-implanted in a silicon wafer,photoluminescence (PL emission) is generated in the energy region in thevicinity of 1 eV, though the mechanism of the PL emission is notclarified (see N. Burger et al., Phys. Rev. Lett., 52, 1645 (1984).However, if the wafer in which the rare gas atoms have beenion-implanted is annealed, the PL emission is caused to disappear,though the reason therefor is again not clear. It is believed that thedisappearance of PL emission is derived from the fact that, since therare gas atom is not chemically bonded with the silicon atom, the raregas atom is diffused within the silicon crystal and may be finallyreleased from the wafer.

Under the circumstances, it can be easily expected that the raregas-containing FT semiconductor or molecule-containing FT semiconductor,which can certainly form the FT structure, may be poor in lower thermalstability. In short, there is a problem that the FT semiconductor willnot be a practical material system.

As described above, the FT semiconductor as a novel band engineeringtechnique can produce the effect of providing a light-emitting functionto an indirect semiconductor. However, there is a problem that the FTsemiconductor in which a closed-shell substance such as a rare gas atomor diatomic molecule is inserted into the interstitial site is poor inthermal stability and is not practical because the closed-shellsubstance is not chemically bonded with the matrix semiconductor.

BRIEF SUMMARY OF THE INVENTION

A light emitting device according to an aspect of the present invention,comprising: an active layer comprising atoms A of a matrix semiconductorhaving a tetrahedral structure, a heteroatom D substituted for the atomA in a lattice site, and a heteroatom Z inserted into an interstitialsite positioned closest to the heteroatom D, the heteroatom D having avalence electron number differing by +1 or −1 from that of the atom A,and the heteroatom Z having an electron configuration of a closed shellstructure through charge compensation with the heteroatom D; and ann-electrode and a p-electrode adapted to supply a current to the activelayer.

A phosphor according to another aspect of the present invention,comprising: atoms A of a matrix semiconductor having a tetrahedralstructure, a heteroatom D substituted for the atom A in a lattice site,and a heteroatom Z inserted into an interstitial site positioned closestto the heteroatom D, the heteroatom D having a valence electron numberdiffering by +1 or −1 from that of the atom A, and the heteroatom Zhaving an electron configuration of a closed shell structure throughcharge compensation with the heteroatom D.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 shows a structure of an FT semiconductor;

FIGS. 2A and 2B show band diagrams of crystalline silicon and He-dopedFT-silicon, respectively;

FIG. 3 shows a band diagram showing change in the band structure ofsilicon having isotropic stretching applied thereto;

FIGS. 4A, 4B and 4C show band diagrams of a quantum dot, a strain effectand an FT semiconductor, respectively;

FIGS. 5A, 5B and 5C are diagrams explaining electron states in the realspace in respect of the X-point conduction band, the Γ-point conductionband and the Γ-point valence band of the energy bands of silicon;

FIGS. 6A, 6B and 6C schematically show change in energy of the X-pointconduction band by the FT structure;

FIG. 7 shows a structure of a pendant type FT semiconductor;

FIGS. 8A, 8B, and 8C show band diagrams of silicon having a PF pairconcentration of zero, a pendant type FT-Si having a PF pairconcentration of 7.8×10²⁰/cm³ and a pendant type FT-Si having a PF pairconcentration of 6.3×10²⁰/cm³, respectively;

FIGS. 9A and 9B are cross-sectional views showing the structures ofsilicon light emitting devices of a vertical type and a lateral type,respectively, according to embodiments;

FIGS. 10A, 10B, 10C and 10D are cross-sectional views showing a methodof forming an active layer of a PF-doped FT-Si according to anembodiment;

FIGS. 11A and 11B are a cross-sectional view and a perspective view,respectively, showing a structure of a silicon light emitting device ofan edge surface emission type according to the fifth embodiment;

FIG. 12 is a graph showing a relationship among a current, voltage andemission intensity of the silicon light emitting device according to thefifth embodiment;

FIGS. 13A and 13B are a cross-sectional view and a perspective view,respectively, showing a structure of a silicon light emitting device ofa surface emission type according to the sixth embodiment;

FIG. 14 is a graph showing a relationship among a current, voltage andemission intensity of the silicon light emitting device according to thesixth embodiment;

FIGS. 15A and 15B are a cross-sectional view and a perspective view,respectively, showing a structure of a silicon light emitting device ofa surface emission type according to the seventh embodiment;

FIG. 16 is a graph showing a relationship among a current, voltage andemission intensity of the silicon light emitting device according to theseventh embodiment;

FIGS. 17A and 17B are a cross-sectional view and a perspective view,respectively, showing a structure of an LD device of an edge surfaceemission type according to the eighth embodiment;

FIG. 18 is a graph showing a relationship between a current and emissionintensity of the LD device according to the eighth embodiment;

FIGS. 19A and 19B are a cross-sectional view and a perspective view,respectively, showing a structure of an LD device of a surface emissiontype according to the ninth embodiment;

FIG. 20 is a graph showing a relationship between a current and emissionintensity of the LD device according to the ninth embodiment;

FIG. 21 is a cross-sectional view showing a structure of a photoelectricdevice array according to the tenth embodiment;

FIG. 22 is graph showing response characteristics of the LD device inthe photoelectric device array according to the tenth embodiment;

FIG. 23 is a cross-sectional view showing a structure of a lightemitting-detecting device array according to the eleventh embodiment;

FIG. 24 is a graph showing response characteristics of the LD device inthe light emitting-detecting device array according to the eleventhembodiment;

FIG. 25 is a cross-sectional view showing a structure of a lightemitting device array according to the twelfth embodiment;

FIGS. 26A and 26B show the input image and the output image,respectively, of the LD device in the light emitting device arrayaccording to the twelfth embodiment;

FIG. 27 is a perspective view showing a structure of an optical devicearray according to the thirteenth embodiment; and

FIG. 28 is a graph showing response characteristics of a photodetectiondevice to input signals supplied from the laser diode (LD device) in theoptical device array according to the thirteenth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The main principle of function of the FT semiconductor (filledtetrahedral semiconductor) according to embodiments of the presentinvention will be described in detail.

Described in the first step are (1) why an indirect semiconductor suchas silicon has an indirect band structure, and (2) why the indirectsemiconductor in non-emissive. Further described briefly are (3) thefeature of the FT semiconductor (rare gas-containing FT semiconductorand molecule-containing FT semiconductor) in comparison with other bandengineering methods, and (4) the principle thereof. Still furtherdescribed is (5) a novel FT semiconductor, i.e., a pendant type FTsemiconductor, which constitutes the important part of the presentinvention.

(1) Band Structure of Indirect Semiconductor:

FIG. 3 shows the band structure of silicon. It is well known to the artthat indirect semiconductors other than silicon have a band structure ofthe shape similar to that shown in FIG. 3. Originally, the main reasonwhy silicon forms an indirect semiconductor resides in that the bondlength d between the adjacent constituent atoms is relatively short. Theenergy difference ΔE between the conduction band and the valence band inthe Γ point is a function of the bond length d and can be representedapproximately by ΔE∝1/d². Therefore, the energy difference ΔE is rapidlydiminished with increase in the bond length d and is changed to beadapted to a direct band structure.

FIG. 3 shows, together with the band structure of the normal lattice,the result of the calculation of the band structure of an imaginarylattice, covering the case where the lattice is stretched through astrain effect in the direction of the crystal axis <111> so as toincrease the Si—Si bond length by 10%. In the drawing, the bandstructures of the normal lattice and of the imaginary lattice aredepicted to permit the upper edges of the valence bands to be matched.

As shown in FIG. 3, if the bond length is increased, the conduction bandis markedly dropped in the Γ point, though a marked change is notobserved in the X point, so as to be changed into a direct bandstructure resembling that of GaAs. Roughly speaking, the energydifference ΔE is diminished because the bond is elongated so as todecrease the repulsion energy between electrons, with the result thatthe conduction band (s-orbital) that is positioned upward in the normallattice is lowered so as to approach the valence band (p-orbital).

(2) Optical Characteristics of an Indirect Semiconductor:

In the indirect semiconductor, the electric dipole transition isoptically forbidden and, thus, the indirect semiconductor is essentiallynon-emissive. On the contrary, the direct semiconductor such as GaAsshows intense interband emission due to electric dipole transition. Thedifference between the two semiconductors is mainly caused by whetherthe two selection rules given below are satisfied.

One of the selection rules relates to the wave number, i.e., therequirement that the energy gap should be made smallest at the specifiedwave number. The other selection rule relates to symmetry of the wavefunction, i.e., the requirement that, in the wave number that makes thegap minimum, one of the conduction band and the valence band should bean even function and the other should be an odd function.

It should be noted in respect of the selection rule of the symmetry thatthe intensity of the emission and the absorption between two levels isgiven by <upper level|transition dipole moment μ|lower level>. In asemiconductor, in which the two levels are represented by the s-orbital(even function) and the p-orbital (odd function) in the vicinity of theatomic orbital, μ denotes an odd function and, thus, the followingrelation is met, which means to be optically allowed:<s|μ|p>=∫even·odd·odd dr≠0.

On the other hand, in a semiconductor, in which the two levels arerepresented by the p-orbital, the following relation is met, which meansto be optically forbidden:<p|μ|p>=∫odd·odd·odd dr=0.

In the direct semiconductor, the gap is made minimum at the Γ point soas to satisfy the selection rule of the wave number. In the opticalsemiconductor, the wave functions of the conduction band and the valenceband are expressed by the s-orbital and the p-orbital, respectively,with the result that the selection rule of the symmetry is alsosatisfied.

On the other hand, in the indirect semiconductor, the conduction bandand the valence band differ from each other in the wave number makingthe gap minimum, resulting in failure to satisfy the selection rule ofthe wave number. In addition, since the wave function for each of theconduction band and the valence band is represented by the p-orbital,the selection rule of the symmetry is not satisfied either. It followsthat the indirect semiconductor is optically forbidden.

(3) FT semiconductor:

As described previously, the FT semiconductor is a theoretic substancethat is discovered in 1984 in the process of calculating the conductionband structure of GaAs. Rompa et al., who discovered the theoreticsubstance, through the band calculation in which the X-point energy isincreased in the FT-GaAs obtained by introducing He into theinterstitial site of GaAs.

In the present invention, the FT semiconductor structure in which theenergy can be controlled at the X-point is applied to an indirectsemiconductor such as silicon so as to impart a light emitting functionto the indirect semiconductor that is originally unlikely to emit light.

The merits of the FT semiconductor as one of the band engineeringmethods will be described in comparison with the quantum dot, and thestrain effect (tensile effect). FIG. 4A shows the band diagram of asilicon quantum dot, FIG. 4B shows the band diagram of silicon to which10% isotropic stretching is applied, and FIG. 4C shows the band diagramof FT-silicon.

The quantum dot extends the conduction band (p-orbital) in the vicinityof the X point to the Γ point through the three dimensional confiningeffect so as to make the gap minimum at the Γ point, thereby changingthe band of the quantum dot into a direct band structure. However, evenupon receipt of the confining effect, the wave functions of theconduction band and the valence band are not basically changed andremain to be the p-orbital, resulting in failure to satisfy theselection rule of symmetry. In short, the optical characteristics of thequantum dot of the indirect semiconductor are derived from pseudoelectric dipole transition where intense emission cannot be expectedunder its effect alone.

The strain effect (tensile effect) permits the conduction band(s-orbital) positioned above the Γ point to be lowered by increasing thebond length by about 10% so as to modulate the band structure into adirect band structure. The band structure thus obtained is very close tothat of the direct semiconductor. The interband transition is electricdipole transition similar to that of a direct semiconductor and, thus,an efficient emission is expected. However, it is considered difficultto stretch the bond length on the order of 10%.

In contrast to the methods described above, the FT semiconductor permitsto raise the conduction band (p-orbital) in the vicinity of the X pointand to lower the conduction band (s-orbital) at the Γ point, therebyrealizing a direct band structure close to that in the case of thedirect semiconductor and the strain effect. The interband transition iselectric dipole transition and, thus, an efficient emission is expected.

(4) Principle of Emission Mechanism of FT Semiconductor:

FIGS. 5A, 5B and 5C show electron states in the real space in respect ofthe X point conduction band (Xc), the Γ point conduction band (Γc) andthe Γ point valence band (Γv), respectively, in the diamond structure ofsilicon.

As shown in FIG. 5A, silicon atoms are positioned at the atomiccoordinates (0, 0, 0) and (1/4, 1/4, 1/4) as viewed in the direction ofthe crystal axis <111> and bonded to each other by the Si—Si bond.Interstitial sites that are called tetrahedral sites are arranged at theatomic coordinates (2/4, 2/4, 2/4) and (3/4, 3/4, 3/4). In thetetrahedral structure, a crystal structure having a relatively largeclearance is formed such that two atoms are arranged, two interstitialsites are arranged, and two atoms are arranged again along the crystalaxis <111>. An atom is not present in the interstitial site. However,since an anti-bonding p-orbital of the silicon atom is expanded towardthe interstitial sites, the state of the anti-bonding p-orbital ispresent in the interstitial sites. “Xc” shown in FIG. 5A denotes theelectron state of the interstitial sites.

In the FT semiconductor, a rare gas atom (or molecule) of the closedshell structure is introduced into the space of the interstitial site soas to realize the FT structure. In this case, the electron in theinterstitial site is excluded, thereby raising the Xc energy as shown inFIG. 4C described above, with the result that the energies of the Γc(anti-bonding s-orbital) and Xc are relatively reversed so as to convertthe indirect band structure into a direct structure. FIG. 6A shows thatthe Xc energy is raised by introducing a rare gas atom into theinterstitial site. The particular phenomenon is considered to be closeto the phenomenon in which the water level is elevated if a substance isplaced in a vessel containing water, as shown in FIGS. 6B and 6C.

If an atom is present in the interstitial site, it is possible that adeep level or a defect level is formed within the band gap. However,since an atom (or molecule) of a closed shell structure having a widegap is inserted into the interstitial site in the FT structure, such alevel is not formed in principle.

(5) Novel Pendant Type FT Semiconductor:

FIG. 7 shows a bonding state of atoms in a novel FT semiconductoraccording to one embodiment of the present invention. The novel FTsemiconductor is referred to as a pendant type FT semiconductor. Thependant type FT semiconductor constituting the main point of the presentinvention comprises atoms A of a matrix semiconductor having atetrahedral structure, a heteroatom D substituted for the atom A in alattice site, and a heteroatom Z inserted into an interstitial sitepositioned closest to the heteroatom D. The heteroatom D has a valenceelectron number differing by +1 or −1 from that of the atom A and can besubstituted for the atom A in the lattice site in the tetrahedralstructure and to be ionized. The heteroatom Z has an electronconfiguration of a closed shell structure through charge compensationwith the heteroatom D to be ionized. Such being the situation, an ionicbond is formed between the heteroatom D and the heteroatom Z so that theheteroatom D performs a function of pinning the heteroatom Z. Thependant type FT semiconductor of this particular structure permitsimproving the thermal stability, thereby overcoming the problem inherentin the rare gas-containing or molecule-containing FT semiconductor. Thisis because, if the heteroatom D and the heteroatom Z are to be pulledaway from each other, electrostatic interaction is exerted between thetwo so as to generate force for maintaining the ionic bond between thetwo.

FIG. 7 shows a pendant type FT semiconductor in which the atom A formingthe matrix semiconductor is silicon, the heteroatom D to be substitutedfor the atom A in the lattice site is phosphorus (P), and the heteroatomZ to be inserted into the interstitial site closest to the heteroatom Dis fluorine (F). The electron configuration of the P atom is1s²2s²2p⁶3s²3p³, and that of the F atom is 1s²2s²2p⁵. A chargecompensation effect is exerted between these two atoms so as to form anionic P⁺—F⁻ bond (PF pair). The P⁺ ion is substituted for the siliconatom in the lattice point so as to assume a tetrahedral structure and,thus, to be stabilized. The F⁻ ion becomes to have an electronconfiguration of a closed shell structure like neon (Ne) and, thus, isalso stabilized.

Where a pendant type FT semiconductor is to be realized by usingsilicon, it is possible to use an n-type or p-type dopant, which hasalready been used in the actual LSI process, as the heteroatom D to besubstituted for the lattice site. This facilitates the manufacture ofthe pendant type FT semiconductor so as to lower the manufacturing costthereof.

Whether a light emitting function can be imparted to the indirectsemiconductor is an important point in the pendant type FT semiconductoraccording to the embodiments of the present invention, as in the raregas-containing or the molecule-containing FT semiconductor. FIGS. 8A, 8Band 8C show the results of the band calculation based on the firstprinciple in respect of a PF-doped FT-Si, in which phosphorus (P) isused as the heteroatom D, and fluorine (F) is used as the heteroatom Z.In order to estimate the influence of the PF pair concentration on theband structure, super cells differing from each other in the number ofPF pairs relative to the number of Si atoms are used for thecalculation. To be more specific, the calculation covered three cases ofFIG. 8A where the number of PF pairs is zero relative to 64 Si atoms(the PF concentration is zero, and the Si atom concentration is5.0×10²²/cm³), FIG. 8B where the number of PF pairs is 1 relative to 63Si atoms (the PF concentration is 7.8×10²⁰/cm³), and FIG. 8C where thenumber of PF pairs is 1 relative to 7 Si atoms (the PF concentration is6.3×10²¹/cm³).

According to the result of the calculation, in the case where the PFpair concentration is zero shown in FIG. 8A, there is the lowest edge ofthe conduction band in the vicinity of Xc, which indicates an indirectband structure inherent in crystalline silicon. In FIG. 8B in which thePF pair concentration is 7.8×10²⁰/cm³, the Xc is scarcely changed, butthe Γc is markedly lowered so as to form the lowest edge of theconduction band, with the result that an indirect band structure isappeared locally inside the substance. In FIG. 8C in which the PF pairconcentration is 6.3×10²¹/cm³, the Xc is markedly raised so as to causethe entire substance to be changed to have an indirect band structure.These results of the calculation indicate that, where the PF pairconcentration is low, the substance locally emits light from the regionhaving the PF pair introduced therein, and that, where the PFconcentration is high, the entire substance emits light.

To be more specific, where the PF pair concentration is 7.8×10²⁰/cm³ orless, e.g., where only one PF pair is present in the crystal, the lowestedge of the conduction band having the PF pair introduced therein ismodulated into the anti-bonding s-orbital. Since the valence band is thebonding p-orbital, the intensity of the emission from the particularsite is given by <s|μ|p>≠0 as described previously in the section (2).It follows that the FT-Si having the PF concentration of 7.8×10²⁰/cm³ orless has a light emitting function.

Also, where the PF pair concentration is 6.3×10²¹/cm³ or more, theregion having the PF pair introduced therein is also modulated into theanti-bonding s-orbital. In addition, the orbitals are positioned closeto each other in the real space so as to overlap each other, therebyforming a band (Γc). Since the intensity of the emission is also givenby the following formula: <s|μ|p>≠0, the FT-Si having the PF pairconcentration of 6.3×10²¹/cm³ or more also exhibits the light emittingfunction.

Where the region has an intermediate PF concentration in a range ofbetween 7.8×10²⁰/cm³ and 6.3×10²¹/cm³, the lowest edge of the conductionband at the site where the PF pair has been introduced is also modulatedinto the anti-bonding s-orbital. In the region having the particular PFpair concentration, the s-orbital is gradually allowed to form a bandwith increase in the PF pair concentration. Since the intensity of theemission is also given by the following formula: <s|μ|p>≠0, the FT-Sihaving the intermediate PF concentration also exhibits the lightemitting function like the FT-Si having the other PF concentration.

In conclusion, the pendant type FT semiconductor is considered toproduce the effect of imparting the light emitting function to theindirect semiconductor regardless of the DZ pair concentration, like therare gas-containing or the molecule-containing FT semiconductor.

In the embodiments of the present invention, the combinations of thematrix semiconductor (constituent atom A), the heteroatom D and theheteroatom Z, which are contained in the pendant type FT semiconductor,include the examples given below:

(1) The matrix semiconductor is selected from the group consisting ofIVb elemental semiconductors and IVb-IVb compound semiconductors, theheteroatom D is selected from the group consisting of Va elements and Vbelements, and the heteroatom Z is selected from the group consisting ofVIIb elements.

(2) The matrix semiconductor is selected from the group consisting ofIVb elemental semiconductors and IVb-IVb compound semiconductors, theheteroatom D is selected from the group consisting of IIIa elements andIIIb elements, and the heteroatom Z is selected from the groupconsisting of Ia elements and Ib elements.

(3) The matrix semiconductor is selected from the group consisting ofIIIb-Vb compound semiconductors, the heteroatom D is selected from thegroup consisting of IVa elements and IVb elements and substituted forthe atom A of IIIb, and the heteroatom Z is selected from the groupconsisting of VIIb elements.

(4) The matrix semiconductor is selected from the group consisting ofIIIb-Vb compound semiconductors, the heteroatom D is selected from thegroup consisting of IIa elements and IIb elements and substituted forthe atom A of IIIb, and the heteroatom Z is selected from the groupconsisting of Ia elements and Ib elements.

(5) The matrix semiconductor is selected from the group consisting ofIIIb-Vb compound semiconductors, the heteroatom D is selected from thegroup consisting of VIa elements and VIb elements and substituted forthe atom A of Vb, and the heteroatom Z is selected from the groupconsisting of VIIb elements.

(6) The matrix semiconductor is selected from the group consisting ofIIIb-Vb compound semiconductors, the heteroatom D is selected from thegroup consisting of IVa elements and IVb elements and substituted forthe atom A of Vb, and the heteroatom Z is selected from the groupconsisting of Ia elements and Ib elements.

The matrix semiconductor can be exemplified as follows. Specifically,the IVb elemental semiconductor is selected from the group consisting ofdiamond, silicon and germanium. The IVb-IVb compound semiconductor isselected from the group consisting of SiC, GeC, Si_(x)Ge_(1-x) (0<x<1)and Si_(x)Ge_(y)C_(1-x-y) (0<x<1, 0<y<1, 0<x+y<1). The IIIb-Vb compoundsemiconductor is selected from the group consisting of BN, BP, AlP,AlAs, AlSb and GaP.

The heteroatom D and the heteroatom Z can be exemplified as follows.Specifically, the Ia element is selected from the group consisting ofLi, Na, K, Rb and Cs. The IIa element is selected from the groupconsisting of Be, Mg, Ca, Sr, and Ba. The IIIa element is selected fromthe group consisting of Sc, Y, La and Lu. The IVa element is selectedfrom the group consisting of Ti, Zr and Hf. The Va element is selectedfrom the group consisting of V, Nb and Ta. The VIa element is selectedfrom the group consisting of Cr, Mo and W. The Ib element is selectedfrom the group consisting of Cu, Ag, and Au. The IIb element is selectedfrom the group consisting of Zn, Cd, and Hg. The IIIb element isselected from the group consisting of B, Al, Ga, In and Tl. The IVbelement is selected from the group consisting of C, Si, Ge, Sn and Pb.The Vb element is selected from the group consisting of N, P, As, Sb,and Bi. The VIb element is selected from the group consisting of O, S,Se and Te. The VIIb element is selected from the group consisting of F,Cl, Br and I.

The light emitting device according to an embodiment of the presentinvention comprises an active layer having an FT structure, and ann-electrode and a p-electrode for exciting the active layer. Thepositions of the n-electrode and the p-electrode relative to the activelayer having the FT structure are not particularly limited. FIGS. 9A and9B are cross-sectional views each showing the structure of a siliconlight emitting device according to an embodiment of the presentinvention.

In the light emitting device of the vertical type shown in FIG. 9A, anactive layer 2 having an FT structure and an insulating film 3 areformed on an n⁺ region 1, and a p⁺ region 4 is formed on the activelayer 2 and the insulating film 3. In other words, the lower and uppersurfaces of the active layer 2 are in contact with the n⁺ region 1 andthe p⁺ region 4, respectively. An n-electrode (not shown) is connectedto the n⁺ region 1, and a p-electrode (not shown) is connected to the p⁺region 4. In this light emitting device, a current flows in the verticaldirection so as to permit electrons to be injected from the n⁺ region 1into the active layer 2 and to permit holes to be injected from the p⁺region 4 into the active layer 2, with the result that the electrons andthe holes are recombined within the active layer 2 of the FT structurehaving a direct band structure so as to emit light.

In the light emitting device of a lateral type shown in FIG. 9B, aburied oxide film 12 is formed in a semi-insulating silicon substrate11, and an n⁺ region 14 and a p⁺ region 15 are formed on the same planeon the oxide film 12 in a manner to have an active layer 13 of the FTstructure sandwiched therebetween. An n-electrode (not shown) isconnected to the n⁺ region 14, and a p-electrode (not shown) isconnected to the p⁺ region 15. In the light emitting device shown inFIG. 9B, a current flows in the lateral direction so as to permit theelectrons to be injected from the n⁺ region 14 into the active layer 13and to permit the holes to be injected from the p⁺ region 15 into theactive layer 13, with the result that the electrons and the holes arerecombined within the active layer 13 of the FT structure having adirect band structure so as to emit light.

In the light emitting device of each of the vertical type and thelateral type, a buried oxide film is formed for preventing the currentleakage. However, it is not absolutely necessary to form the buriedoxide film in the case where the current leakage can be prevented by anyof the element structure, the substrate resistivity and the circuitstructure.

Each of FIGS. 9A and 9B shows the basic structure of the light emittingdevice, and various structures of the specific light emitting device areconceivable. For example, in the light emitting device according to anembodiment of the present invention, it is possible for the emittedlight to be taken out from the edge surface or from the upper surface ofthe active layer. Where the emitted light is taken out from the uppersurface of the active layer, a transparent electrode may be formed onthe upper surface of the active layer. It is also possible to use anoptical resonator of a pair of mirror surfaces, i.e., a pair of alow-reflectance mirror surface and a high-reflectance mirror surface,which are formed to have the active layer sandwiched therebetween, so asto cause a laser oscillation. It is also possible to combine thesestructures appropriately. Further, a light emitting device array can bemanufactured by forming a plurality of light emitting devices integrallyon the same substrate. A photoelectric device array can be manufacturedby forming a light emitting device and a transistor integrally on thesame substrate. A light emitting-detecting device array can bemanufactured by forming a light emitting device and a photodetectiondevice integrally on the same substrate. An optical device array can bemanufactured by forming a light emitting device, a photodetection deviceand a waveguide connecting these light emitting device andphotodetection device integrally on the same substrate. Thesemodifications will be described herein later in detail.

The method of forming an active layer having an FT structure will now bedescribed with reference to FIGS. 10A, 10B, 10C and 10D. The followingdescription covers the case of forming an active layer of PF-dopedFT-Si.

In the first step, a Si wafer 21 is prepared as shown in FIG. 10A,followed by doping a prescribed doping region 22 of the Si wafer 21 withphosphorus (P) as a heteroatom D, as shown in FIG. 10B. Phosphorus (P)performs the function of an n-type dopant.

In the next step, fluorine (F⁺) as a heteroatom Z is ion-implanted intothe prescribed doping region 22 of the Si wafer 21 already doped with P,as shown in FIG. 10C. In this ion implantation process, the energy, thedose, the orientation of the substrate surface, the tilted angle, thesubstrate temperature, and so forth are made optimum. The F⁺ ion, whichis originally an active ion species, receives an excessive electronowned by the P atom and an electron supplied from the ground through thesubstrate to be in an F⁻ ion, thereby forming a closed shell structurelike the neon (Ne) atom and being inactivated chemically.

In the step shown in FIG. 10D, annealing is carried out so as torecrystallize the lattice disturbed by the ion implantation, therebyforming an active layer 23 consisting of FT-Si. In this annealingprocess, the silicon atom in the lattice point can be replaced by the Patom and the F atom can be inserted into the interstitial site bycontrolling the annealing temperature, the annealing time, theatmosphere and so forth. The P atom is positioned in the lattice point.However, since the P atom is deprived of an electron by the F atom, theactive layer 23 is made electrically inactive and, thus, the resistivityof the active layer 23 is increased. The P atom and the F atom arebonded to each other by an ionic bond and are not dissociated even by atemperature elevation accompanying the annealing treatment, so as tomaintain the paired state.

Further, the other steps are carried out so as to manufacture the lightemitting device constructed as shown in FIG. 9A or 9B.

As described above, an active layer having an FT structure can be formedwithin a matrix semiconductor by the method employing the ionimplantation and the annealing in combination. Incidentally, it is alsopossible to form the active layer having the FT structure by thecombination of a thermal diffusion and the annealing. Further, theactive layer having the FT structure can be formed by employing othermethods.

If the heteroatom D at the lattice point is bonded to the heteroatom Zin the interstitial site like the PF pair, another inherent vibrationmode differing from the lattice vibration of the matrix semiconductor isgenerated. As a result, it is possible to analyze directly the FTstructure from infrared spectroscopy or Raman spectroscopy. When itcomes to an example of the PF pair, the calculation of the standardvibration indicates that a vibration mode appears in the vicinity of thewave number of 150 to 200 cm⁻¹. In this fashion, evaluation of thevibration mode provides one of effective means of examining the presenceof the FT structure.

As an indirect and simple method of detecting the presence of the DZpair, it is possible to employ an electrical measurement such asresistance measurement or Hall measurement. In the case of using ann-type or p-type dopant as the heteroatom D substituted for the latticepoint, the substrate before doping the heteroatom Z in the interstitialsite exhibits an n-type or p-type and, thus, has a low resistivity. Ifthe heteroatom D is paired with the heteroatom Z, the free carrier isdecreased by the charge compensation between the heteroatom Z and theheteroatom Z so as to increase the resistivity of the substrate. Thus,it is possible to detect whether the DZ pair has been formed bycomparing the resistances or the carrier concentrations before and afterthe doping of the heteroatom Z.

It is also possible to pulverize the pendant type FT semiconductoraccording to an embodiment of the present invention so as to use thepulverized FT semiconductor as a phosphor. The combinations of thematrix semiconductor (constituent atom A), the heteroatom D and theheteroatom Z of the phosphor are as described previously in conjunctionwith the active layer.

The present invention will be described in more detail with reference tospecific embodiments.

First Embodiment

A silicon light emitting device of the vertical type, which isconstructed as shown in FIG. 9A, will be described. The PF doped FT-Siactive layer is formed by using silicon as the matrix semiconductor, theP atom as the heteroatom D substituted for the lattice site, and the Fatom as the heteroatom Z inserted into the interstitial site. The PFpair concentration is 2.5×10²⁰/cm³. The concentration of each of the Patoms and the F atoms can be confirmed by SIMS.

For examining whether a PF pair of a pendant type FT structure is formedin the active layer, it is effective to examine the vibration modeinherent in the PF pair, and the PF pair can be detected by themicrospectroscopy of the active layer. As a method of easily checkingthe PF pair formation, it is possible to prepare a PF-doped regionhaving a composition equal to that of the active layer and a regiondoped with P alone on the surface of a substrate having a highresistivity so as to compare these two doped regions in respect of thesheet resistance or the carrier concentration. If a PF pair is formed,the charge compensation is caused so as to increase the resistivity anddecrease the carrier concentration of the PF-doped region, compared withthe region doped with P alone.

If the PF-doped FT-Si in the active layer is excited with light, PLemission is generated in the wavelength region corresponding to the bandgap of the crystalline silicon. As apparent from the result of the bandcalculation shown in FIGS. 8A and 8B, the band gap of the PF-doped FT-Siis substantially equal to that of the crystalline silicon. Therefore,the PL emission wavelength is not contradictory to the emissionwavelength expected from the result of the calculation described above.It follows that an FT-Si is considered to be formed in the active layerso as to change the active layer into a direct band structure.

If the light emitting device is driven by a current so as to permitholes to be injected from the p⁺ region into the active layer and topermit electrons to be injected from the n⁺ region into the activelayer, it is possible to bring about a recombination radiation excitedwith current.

As described above, the pendant type FT semiconductor for modulating theenergy band into a direct structure is highly effective as a bandengineering method for imparting a light emitting function to theindirect semiconductor.

COMPARATIVE EXAMPLE

Described in the following is an element exactly equal in structure tothe first embodiment, except that the B atom is used in place of the Fatom as the heteroatom Z inserted into the interstitial site in theactive layer. The B concentration is set at 2.5×10²⁰/cm³, which is equalto the F concentration in the first embodiment.

The element of the Comparative Example is non-emissive even if a currentis applied thereto. Also, the element of the Comparative Example isnon-emissive even if the active layer is excited with light.

The reason why the element of the Comparative Example is non-emissive isdue to the position of the B atom in the crystal. As widely known to theart, the B atom is a typical p-type dopant and is positioned at thelattice site, not at the interstitial site. As a result, the B atom andthe P atom perform charge compensation so as to increase the resistivityof the active layer. However, the pendant type FT structure is notformed.

As described above, in order to form a pendant type FT structure and toinduce a direct band structure in the matrix semiconductor, it isnecessary to select the heteroatoms with a sufficient attention paid tothe combination of the heteroatom substituted for the lattice site andthe heteroatom inserted into the interstitial site.

Second Embodiment

A light emitting device of the structure equal to that of the firstembodiment is prepared except that the B atom of a p-type dopant is usedas the heteroatom D and the K atom is used as the heteroatom Z. Each ofthe B concentration and the K concentration as determined by SIMS is5×10²⁰/cm³, and the BK pair concentration is estimated at 5×10²⁰/cm³.

When the light emitting device is excited with light, PL emission iscaused at the wavelength in the vicinity of the band gap of thecrystalline silicon. When the element is driven with current, it ispossible to bring about a current injection radiation from the region ofthe FT structure in the active layer. The emission wavelength is alsoequal to the wavelength in the vicinity of the band gap of thecrystalline silicon, and the emitted light exhibits emission spectrum ofa shape resembling the PL emission spectrum.

As apparent from the second embodiment, the light emitting function canbe imparted to the indirect semiconductor even in the case where theheteroatom D and the heteroatom Z represent a combination of a IIIbelement and a Ia element.

Third Embodiment

Light emitting devices are manufactured as in the first embodiment byusing various materials as the matrix semiconductor, the heteroatom D atthe lattice site and the heteroatom Z at the interstitial site.

Table 1 shows (1) the matrix semiconductor in the active layer, (2) thelattice site substituted by the heteroatom D, (3) the heteroatom Dsubstituted for the lattice site, (4) the heteroatom Z inserted into theinterstitial site, (5) the DZ pair concentration estimated from the Zconcentration, and (6) the emission peak wavelength through currentinjection.

As shown in Table 1, emission through the current injection is causedeven in compound indirect semiconductors by introducing a pendant typeFT structure into the compound-based indirect semiconductor. TABLE 1 (2)(5) (6) (1) Lattice site DZ pair Emission Matrix substituted by D (3)(4) concentration wavelength semiconductor (group) D (group) Z (group)(/cm³) (nm) AlP P (Vb) Si (IVb) Na (Ia) 1.5E+20 515 GaP Ga (IIIb) Mg(IIa) Na (Ia) 2.1E+20 560 GaP Ga (IIIb) Si (IVb) F (VIIb) 1.4E+20 560GaP Ga (IIIb) Mg (IIa) K (Ia) 4.4E+20 565 GaP Ga (IIIb) Zn (IIb) Na (Ia)3.6E+20 565 GaP P (Vb) Se (VIb) F (VIIb) 8.8E+19 565 GaP P (Vb) S (VIb)F (VIIb) 1.0E+20 570 GaP P (Vb) S (VIb) Cl (VIIb) 9.7E+19 570 AlSb Sb(Vb) Se (VIb) F (VIIb) 6.2E+20 785 AlSb Sb (Vb) Te (VIb) F (VIIb)5.1E+20 790

Fourth Embodiment

A silicon light emitting device of the lateral type, which isconstructed as shown in FIG. 9B, will be explained. Specifically, aPF-doped FT-Si active layer is formed by using silicon as the matrixsemiconductor, the P atom as the heteroatom D substituted for thelattice site, and the F atom as the heteroatom Z inserted into theinterstitial site. The PF pair concentration is 4.6×10²⁰/cm³. Theconcentration of each of P atoms and the F atoms is confirmed by SIMS.

For examining whether the PF pair of the pendant type FT structure isformed in the active layer, it is effective to examine the vibrationmode inherent in the PF pair. Also, the PF pair formation can bedetected for convenience from the resistance value or the carrierconcentration.

When the light emitting device is driven with current, it is possible topermit emission through the current injection to be generated from theregion of the FT structure in the active layer. The emission isgenerated in the vicinity of the band gap of the crystalline silicon.

As described above, it is possible to permit the light emitting devicehaving the FT structure introduced therein to cause emission throughcurrent injection by the lateral current driving as in the case of thevertical current driving.

Fifth Embodiment

FIGS. 11A and 11B are a cross-sectional view and a perspective view,respectively, showing the structure of the silicon light emitting deviceof an edge surface emission type according to this embodiment. A buriedoxide film 32 is formed within a semi-insulating silicon substrate 31.An n⁺ region 33 doped with P, an active layer 34 of an FT-Si, and a p⁺region 35 doped with B are formed on the upper surface of the buriedoxide film 32. The active layer 34 consists of the PF-doped FT-Si inwhich a matrix silicon layer is doped with the P atom used as theheteroatom D substituted for the lattice site and with the F atom usedas the heteroatom Z inserted into the interstitial site. The PF pairconcentration is about 3×10²⁰/cm³. The p⁺ region 35, the active layer 34and the n⁺ region 33 are partly etched, and an n-electrode 36 connectedto the n⁺ region 33 and a p-electrode 37 connected to the p⁺ region 35are formed. Each of the n-electrode 36 and the p-electrode 37 is formedof Ni silicide/Au. As shown in FIG. 11B, one edge surface of the lightemitting device is coated with a non-reflective film NR, and the otheredge surface is coated with a reflective film R. In the structure,emission through current injection can be achieved efficiently from theedge surface coated with the non-reflective film NR.

When the light emitting device is driven with current, the emissionthrough current injection radiation is caused. FIG. 12 is a graphshowing the relationship among the current, voltage and the emissionintensity.

As described above, it is possible to manufacture a silicon lightemitting device of the edge surface emission type having the FTstructure introduced therein and to permit the light emitting device togenerate the emission through the current injection.

Sixth Embodiment

FIGS. 13A and 13B are a cross-sectional view and a perspective view,respectively, showing the structure of the silicon light emitting deviceof a surface emission type according to this embodiment. A buried oxidefilm 42 is formed within a semi-insulating silicon substrate 41. An n⁺region 43 doped with P and an active layer 44 consisting of FT-Si areformed on the upper surface of the buried oxide film 42. The activelayer 44 consists of PF-doped FT-Si in which a matrix silicon layer isdoped with the P atom used as the heteroatom D substituted for thelattice site and with the F atom used as the heteroatom Z inserted intothe interstitial site. The PF pair concentration is about 7×10²⁰/cm³. Aninsulating layer 45 is formed selectively on the upper surface of theactive layer 44, and a p⁺ region 46 doped with B is formed to cover theinsulating layer 45. The p⁺ region 46, the insulating layer 45, theactive layer 44 and the n⁺ region 43 are partly etched, and ann-electrode 47 connected to the n⁺ region 43 and a p-electrode 48connected to the p⁺ region 46 are formed. The p-electrode 48 is arrangedabove the insulating layer 45. Each of the n-electrode 47 and thep-electrode 48 is formed of Ni silicide/Au. In the light emitting devicein this embodiment, EL emission is taken out from the upper surfacethrough the p⁺ region 46. Therefore, the light emitting device isdesigned to diminish or eliminate substantially completely the overlapbetween the active layer 44 and the p-electrode 48 as viewed from thesurface so as to prevent the active layer 44 from being concealed by thep-electrode 48. A non-reflective film 49 is formed on the p⁺ region 48on the front surface, and a reflective film 50 is formed on the rearsurface of the substrate 41. Each of the edge surfaces of the lightemitting device is coated with a reflective film. In the structure shownin the drawings, emission through current injection can be achievedefficiently from the non-reflective film 49 on the side of the frontsurface.

When the light emitting device is driven with current, electrons andholes are recombined within the active layer 44 consisting of the FT-Siso as to generate emission through the current injection. FIG. 14 is agraph showing the relationship among the current, the voltage and theemission intensity.

As described above, it is possible to manufacture a silicon lightemitting device of the surface emission type having the FT structureintroduced therein and to permit the light emitting device to generatethe emission through the current injection.

Seventh Embodiment

FIGS. 15A and 15B are a cross-sectional view and a perspective view,respectively, showing the structure of the silicon light emitting deviceof a surface emission type according to this embodiment. This lightemitting device is substantially equal to the light emitting device ofthe sixth embodiment, except that an auxiliary electrode 51 and atransparent electrode 52 are formed in place of the non-reflective film49.

When the light emitting device is driven with current, electrons andholes are recombined within the active layer 44 consisting of an FT-Siso as to generate emission through current injection. FIG. 16 is a graphshowing the relationship among the current, the voltage and the emissionefficiency.

As described above, it is possible to manufacture a silicon lightemitting device of the surface emission type by introducing an FTstructure and using a transparent electrode and to permit the lightemitting device to generate the emission through the current injection.

Eighth Embodiment

FIGS. 17A and 17B are a cross-sectional view and a perspective view,respectively, showing the structure of the laser diode (herein afterreferred to as “LD device”) of an edge surface emission type accordingto this embodiment. The LD device is an edge surface light emittingdevice having a ridge waveguide structure. A buried oxide film 62 isformed within a semi-insulating silicon substrate 61. An n⁺ region 63doped with P, an active layer 64 consisting of FT-Si, and a p⁺ region 65doped with B are formed on the upper surface of the buried oxide film62. The active layer 64 consists of PF-doped FT-Si having the P atomdoped as a heteroatom D for the lattice site and the F atom doped as aheteroatom Z at the interstitial site. The PF pair concentration isabout 1×10²¹/cm³. The p⁺ region 65, the active layer 64 and the n⁺region 63 are partly etched, and an n-electrode 66 connected to the n⁺region 63 and a p-electrode 67 connected to the p⁺ region 65 are formed.Further, the p-electrode 67 and the p⁺ region 65 are partly etched. Eachof the n-electrode 66 and the p-electrode 67 is formed of Nisilicide/Au. As shown in FIG. 17B, a dielectric multi-layered mirror LRhaving a low reflectance is formed on one edge surface of the LD device,and a dielectric multi-layered mirror HR having a high reflectance isformed on the other edge surface of the LD device.

When the LD device is driven with current, it is possible that laserlight is oscillated from the edge surface. FIG. 18 is a graph showingthe relationship between the current and the emission intensity. If theemission spectrum generated by the current injection is examined, it isfound that the spectrum is broad under a current lower than thethreshold current, but is made sharp and monochromatic under a currenthigher than the threshold current, though the particular change in thespectrum is not shown in the drawing. The particular change in thespectrum indicates that it is possible to generate a continuous laseroscillation under a current higher than the threshold current.

Various materials other than those described above can be used as the FTsemiconductor materials constituting the active layer. For example, itis possible to use the B atom as the heteroatom D and the K atom as theheteroatom Z in combination with Si used as the matrix semiconductor. Itis also possible to use various combinations of the materials describedpreviously.

Ninth Embodiment

FIGS. 19A and 19B are a cross-sectional view and a perspective view,respectively, showing the structure of the surface emission type LDdevice according to this embodiment. A buried oxide film 72 is formedwithin a semi-insulating silicon substrate 71. An n⁺ region 73 dopedwith P and an active layer 74 consisting of an FT-Si are formed on theupper surface of the buried oxide film 72. The active layer 74 is formedof PF-doped FT-Si having the P atom doped at the lattice site as theheteroatom D and having the F atom doped at the interstitial site as theheteroatom Z. The PF pair concentration is about 7×10²⁰/cm³. Aninsulating film 75 is formed selectively on the upper surface of theactive layer 74, and a p⁺ region 76 doped with B is formed to cover theinsulating layer 75. The p⁺ region 76, the insulating film 75, theactive layer 74 and the n⁺ region 73 are partly etched, and ann-electrode 77 connected to the n⁺ region 73 and a p-electrode 78connected to the p⁺ region 76 are formed. Each of the n-electrode 78 andthe p-electrode 78 is formed of Ni silicide/Au. The p-electrode 78 ispartly etched, and a dielectric multi-layered mirror 79 of a lowreflectance is formed. A dielectric multi-layered mirror 80 of a highreflectance is formed on the rear surface of the substrate 71 in amanner to correspond to the dielectric multi-layered mirror 79 of a lowreflectance.

When the LD device is driven with current, it is possible to permitlaser light to be oscillated from the surface. FIG. 20 is a graphshowing the relationship between the current and the emission intensity.Laser oscillation can be generated continuously under a current higherthan the threshold current shown in FIG. 20.

Tenth Embodiment

FIG. 21 shows the structure of the photoelectric device array accordingto this embodiment. The photoelectric device array is prepared byforming on the same substrate an integrated circuit consisting of alight emitting device and a switching device (MOS transistor) adapted tomodulate the light output of the light emitting device. The lightemitting device consists of a surface emission LD device having thestructure equal to that of the ninth embodiment. On the other hand, ap-well region 81, an n⁺-type source and drain regions 82, 83 are formedon the buried oxide film 72 formed within the substrate 71. A gateelectrode 85 is formed on a gate insulating film 84 between the sourceand drain regions 82, 83. A source electrode 86 and a drain electrode 87are formed on the source region 82 and the drain region 83,respectively. Further, an n-electrode 77 of the LD device and the drainelectrode 87 of the MOS transistor are connected to each other via awire 88.

FIG. 22 is a graph showing the modulated signal (electric signal)supplied to the transistor and the response of the output lightgenerated from the LD device. As apparent from FIG. 22, the output lightis modulated under the frequency of 10 GHz relative to the high-speedmodulated signal of 10 GHz. This indicates that the photoelectric devicearray in this embodiment permits the high-speed direct modulation.Although a costly light modulation element is required in the past forcoding the output of the LD device, it is unnecessary to use a lightmodulation element in this embodiment of the present invention.

Eleventh Embodiment

FIG. 23 shows the structure of the light emitting-detecting device arrayaccording to this embodiment. The light emitting-detecting device arrayis prepared by forming on the same substrate an integrated circuitconsisting of a photodetection device and a light emitting device. Thelight emitting-detecting device array produces the functions ofprocessing the received optical signal and outputting the result of theprocessing as a new optical signal. The light emitting device is formedof a surface emission LD device constructed like the LD device accordingto the ninth embodiment. On the other hand, the photodetection device isformed of a germanium photodetection device. An n⁺ layer 91, an i-layer92, and a p⁺ layer 93 are formed on the buried oxide film 72 formedwithin the substrate 71. The p⁺ layer 93, the i-layer 92, and the n⁺layer 91 are partly etched so as to form an n-electrode 94 that isconnected to the n⁺ layer 91. A p-electrode 95 is formed on the p⁺ layer93. The p-electrode 95 is partly etched, and a non-reflective layer 96is formed. The photodetection device and the light emitting device areconnected in series via a wire 97. The light emitting-detecting devicearray has a relaying function for outputting the input optical signalwith its waveform left unchanged.

FIG. 24 is a graph showing the optical signal supplied to thephotodetection device and having a wavelength of 850 nm and response ofthe output light generated from the LD device. As apparent from FIG. 24,an output light of the same waveform is obtained relative to an inputsignal modulated under the frequency of 5 GHz. In this fashion, thelight emitting-detecting device array in this embodiment permits asignal relay at a high speed.

Twelfth Embodiment

FIG. 25 shows the structure of the light emitting device array accordingto this embodiment. In this light emitting device array, plural lightemitting devices are formed integrally on the same substrate foroptically outputting an image signal. Each of the plural light emittingdevices is equal to the surface emission type LD device constructed asin the ninth embodiment. The plural light emitting devices are connectedto each other via a wire 99.

FIGS. 26A and 26B show an image signal (electric signal) supplied to theLD device array and an output image (optical signal) generated from theLD device array. As apparent from FIGS. 26A and 26B, it is possible toobtain an output image reproducing the input image with a high fidelity.

Thirteenth Embodiment

FIG. 27 shows the structure of the optical device array according tothis embodiment. In this optical device array, a light emitting device,a photodetection device and a waveguide for connecting thephotodetection device and the light emitting device are formedintegrally on the same substrate. The optical device array permitsgenerating, transmitting and receiving an optical signal.

As shown in FIG. 27, an edge surface emission type LD device 110 forgenerating a signal and a germanium photodetection device 120 forreceiving the signal are formed on a silicon substrate 101. An oxidefilm 102 is formed between the LD device 110 and the photodetectiondevice 120, and a Si waveguide 130 for transmitting the optical signalis formed on the oxide film 102. The edge surface emission type LDdevice 110 is equal in structure to that of the eighth embodiment. Then-electrode 66 and the p-electrode 67 are shown in FIG. 27. A trench isformed in the substrate 101 in the vicinity of the LD device 110 so asto expose the edge surface to the outside. FIG. 27 also shows ann-electrode 121 and a p-electrode 122 in respect of the germaniumphotodetection device 120.

FIG. 28 is a graph showing the optical signal generated from the LDdevice and the output response of the photodetection device. As apparentfrom FIG. 28, the output signal is modulated under the frequency of 50GHz relative to the high-speed modulated signal under the frequency of50 GHz. In this fashion, the optical device array in this embodimentpermits transmission of an optical signal at a high speed. It istechnically impossible in the past to form on a wafer an optical wiringunit for transmitting an optical signal. However, this embodiment makesit possible to form such an optical wiring unit.

Fourteenth Embodiment

A phosphor that can be excited by a light source, an electron source oran X-ray source will be described. The phosphor is in the form of apowdery crystal containing an FT semiconductor as a main component. TheFT semiconductor consists of an NF-doped FT-SiC comprising siliconcarbide (SiC) as the matrix semiconductor, the N atom as the heteroatomD and F atom as the heteroatom Z. The NF concentration is adjusted atthree levels of 9×10¹⁷/cm³, 1.2×10¹⁹/cm³, and 1.6×10²⁰/cm³.

The band gap is estimated at about 3 eV from the band calculation of theNF-doped FT-SiC, and a blue emission is expected to be generated. Also,since the interband transition is electric dipole transition, theemission recombination life is expected to be short so as to achieveintense emission efficiently.

When the phosphor is excited with light such as an ultraviolet light, itis possible to obtain blue PL emission. Where the emission intensity ofthe PL emission spectrum relative to the NF pair concentration isexamined, it is found that the number of NF pairs tends to beproportional to the emission intensity. Such being the situation, the NFpairs are considered to act as localized luminescent centers.

Various materials other than those described above can be used as thematerials of the phosphor. For example, it is possible to use the B atomas the heteroatom D and the K atom as the heteroatom Z in the case wherethe matrix semiconductor is formed of SiC. It is also possible to usethe O atom as the heteroatom D and the F atom as the heteroatom Z in thecase where the matrix semiconductor is formed of BP. It is also possibleto use the various combinations of the materials described previously.

Fifteenth Embodiment

The phosphor in this embodiment is formed of an AlNa-doped FT-SiCcomprising silicon carbide (SiC) used as the matrix semiconductor, theAl atom used as the heteroatom D and the Na atom used as the heteroatomZ. The AlNa concentration is about 5×10²⁰/cm³.

The band gap is estimated at about 3 eV from the band calculation of theAlNa-doped FT-SIC, and a blue emission is expected to be generated. Whenthe PL emission is examined, it is possible to obtain a blue-greenemission, which is substantially coincident with the estimation based onthe calculation.

Sixteenth Embodiment

Phosphors are obtained as in the fourteenth and fifteenth embodiments byusing various materials as the matrix semiconductor, the heteroatom Dsubstituted for the lattice site and the heteroatom Z inserted into theinterstitial site.

Table 2 shows (1) the matrix semiconductor of the phosphor, (2) thelattice site substituted by the heteroatom D, (3) the heteroatom Dsubstituted for the lattice site, (4) the heteroatom Z inserted into theinterstitial site, (5) the DZ pair concentration estimated from the Zconcentration, and (6) the PL emission wavelength.

As shown in Table 2, the PL emission can be generated efficiently byintroducing the pendant type FT structure into an indirectsemiconductor. TABLE 2 (2) (5) (6) (1) Lattice site DZ pair EmissionMatrix substituted by D (3) (4) concentration wavelength semiconductor(group) D (group) Z (group) (/cm³) (nm) AlP P (Vb) Si (IVb) Na (Ia)6.0E+20 520 GaP Ga (IIIb) Si (IVb) F (VIIb) 3.0E+20 560 GaP Ga (IIIb) Mg(IIa) K (Ia) 2.3E+20 565 GaP Ga (IIIb) Zn (IIb) Na (Ia) 5.2E+20 570 GaPP (Vb) Se (VIb) F (VIIb) 4.0E+20 570 AlAs P (Vb) Se (VIb) F (VIIb)5.1E+20 590 AlSb Sb (Vb) Se (VIb) F (VIIb) 6.0E+20 785 AlSb Sb (Vb) Te(VIb) F (VIIb) 5.5E+20 790

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A light emitting device, comprising: an active layer comprising atomsA of a matrix semiconductor having a tetrahedral structure, a heteroatomD substituted for the atom A in a lattice site, and a heteroatom Zinserted into an interstitial site positioned closest to the heteroatomD, the heteroatom D having a valence electron number differing by +1from that of the atom A, and the heteroatom Z having an electronconfiguration of a closed shell structure through charge compensationwith the heteroatom D; and an n-electrode and a p-electrode adapted tosupply a current to the active layer.
 2. A light emitting device,comprising: an active layer comprising atoms A of a matrix semiconductorhaving a tetrahedral structure, a heteroatom D substituted for the atomA in a lattice site, and a heteroatom Z inserted into an interstitialsite positioned closest to the heteroatom D, the heteroatom D having avalence electron number differing by −1 from that of the atom A, and theheteroatom Z having an electron configuration of a closed shellstructure through charge compensation with the heteroatom D; and ann-electrode and a p-electrode adapted to supply a current to the activelayer.
 3. The light emitting device according to claim 1, wherein thematrix semiconductor is selected from the group consisting of IVbelemental semiconductors and IVb-IVb compound semiconductors, theheteroatom D is selected from the group consisting of Va elements and Vbelements, and the heteroatom Z is selected from the group consisting ofVIIb elements.
 4. The light emitting device according to claim 2,wherein the matrix semiconductor is selected from the group consistingof IVb elemental semiconductors and IVb-IVb compound semiconductors, theheteroatom D is selected from the group consisting of IIIa elements andIIIb elements, and the heteroatom Z is selected from the groupconsisting of Ia elements and Ib elements.
 5. The light emitting deviceaccording to claim 1, wherein the matrix semiconductor is selected fromthe group consisting of IIIb-Vb compound semiconductors, the heteroatomD is selected from the group consisting of IVa elements and IVb elementsand substituted for the atom A of IIIb, and the heteroatom Z is selectedfrom the group consisting of VIIb elements.
 6. The light emitting deviceaccording to claim 2, wherein the matrix semiconductor is selected fromthe group consisting of IIIb-Vb compound semiconductors, the heteroatomD is selected from the group consisting of IIa elements and IIb elementsand substituted for the atom A of IIIb, and the heteroatom Z is selectedfrom the group consisting of Ia elements and Ib elements.
 7. The lightemitting device according to claim 1, wherein the matrix semiconductoris selected from the group consisting of IIIb-Vb compoundsemiconductors, the heteroatom D is selected from the group consistingof VIa elements and VIb elements and substituted for the atom A of Vb,and the heteroatom Z is selected from the group consisting of VIIbelements.
 8. The light emitting device according to claim 2, wherein thematrix semiconductor is selected from the group consisting of IIIb-Vbcompound semiconductors, the heteroatom D is selected from the groupconsisting of IVa elements and IVb elements and substituted for the atomA of Vb, and the heteroatom Z is selected from the group consisting ofIa elements and Ib elements.
 9. The light emitting device according toclaim 1, further comprising: an n-layer formed between the active layerand the n-electrode so as to be in contact with the active layer, and ap-layer formed between the active layer and the p-electrode so as to bein contact with the active layer, wherein the n-layer, the active layerand the p-layer are laminated one upon the other.
 10. The light emittingdevice according to claim 1, further comprising: an n-layer formedbetween the active layer and the n-electrode so as to be in contact withthe active layer, and a p-layer formed between the active layer and thep-electrode so as to be in contact with the active layer, wherein then-layer, the active layer and the p-layer are arranged in-plane.
 11. Thelight emitting device according to claim 1, further comprising anon-reflective film formed on one edge surface of the active layer and areflective film formed on the other edge surface of the active layer.12. The light emitting device according to claim 1, wherein then-electrode or the p-electrode is arranged as a surface electrode, and anon-reflective film is formed in an upper portion of the active layerwhich is not covered with the surface electrode and a reflective film isformed in a lower portion of the active layer so as to face thenon-reflective layer.
 13. The light emitting device according to claim1, wherein the n-electrode or the p-electrode is arranged as a surfaceelectrode, and the surface electrode is transparence.
 14. The lightemitting device according to claim 1, further comprising an opticalresonator having a pair of mirror surfaces arranged to have the activelayer sandwiched therebetween in a in-plane direction of the activelayer and differing from each other in reflectance.
 15. The lightemitting device according to claim 1, further comprising an opticalresonator having a pair of mirror surfaces arranged to have the activelayer sandwiched therebetween in a vertical direction to a plane of theactive layer and differing from each other in reflectance.
 16. Aphotoelectric device array, comprising the light emitting deviceaccording to claim 1, and a transistor, which are formed on the samesubstrate.
 17. A light emitting-detecting device array, comprising thelight emitting device according to claim 1, and a photodetection device,which are formed on the same substrate.
 18. A light emitting devicearray, comprising a plurality of the light emitting devices according toclaim 1, which are formed on the same substrate.
 19. An optical devicearray, comprising the light emitting device according to claim 1, aphotodetection device, and a waveguide connecting the light emittingdevice with the photodetection device, which are formed on the samesubstrate.
 20. A phosphor, comprising: atoms A of a matrix semiconductorhaving a tetrahedral structure, a heteroatom D substituted for the atomA in a lattice site, and a heteroatom Z inserted into an interstitialsite positioned closest to the heteroatom D, the heteroatom D having avalence electron number differing by +1 from that of the atom A, and theheteroatom Z having an electron configuration of a closed shellstructure through charge compensation with the heteroatom D.
 21. Aphosphor, comprising: atoms A of a matrix semiconductor having atetrahedral structure, a heteroatom D substituted for the atom A in alattice site, and a heteroatom Z inserted into an interstitial sitepositioned closest to the heteroatom D, the heteroatom D having avalence electron number differing by −1 from that of the atom A, and theheteroatom Z having an electron configuration of a closed shellstructure through charge compensation with the heteroatom D.
 22. Thephosphor according to claim 20, wherein the matrix semiconductor isselected from the group consisting of IVb elemental semiconductors andIVb-IVb compound semiconductors, the heteroatom D is selected from thegroup consisting of Va elements and Vb elements, and the heteroatom Z isselected from the group consisting of VIIb elements.
 23. The phosphoraccording to claim 21, wherein the matrix semiconductor is selected fromthe group consisting of IVb elemental semiconductors and IVb-IVbcompound semiconductors, the heteroatom D is selected from the groupconsisting of IIIa elements and IIIb elements, and the heteroatom Z isselected from the group consisting of Ia elements and Ib elements. 24.The phosphor according to claim 20, wherein the matrix semiconductor isselected from the group consisting of IIIb-Vb compound semiconductors,the heteroatom D is selected from the group consisting of IVa elementsand IVb elements and substituted for the atom A of IIIb, and theheteroatom Z is selected from the group consisting of VIIb elements. 25.The phosphor according to claim 21, wherein the matrix semiconductor isselected from the group consisting of IIIb-Vb compound semiconductors,the heteroatom D is selected from the group consisting of IIa elementsand IIb elements and substituted for the atom A of IIIb, and theheteroatom Z is selected from the group consisting of Ia elements and Ibelements.
 26. The phosphor according to claim 20, wherein the matrixsemiconductor is selected from the group consisting of IIIb-Vb compoundsemiconductors, the heteroatom D is selected from the group consistingof VIa elements and VIb elements and substituted for the atom A of Vb,and the heteroatom Z is selected from the group consisting of VIIbelements.
 27. The phosphor according to claim 21, wherein the matrixsemiconductor is selected from the group consisting of IIIb-Vb compoundsemiconductors, the heteroatom D is selected from the group consistingof IVa elements and IVb elements and substituted for the atom A of Vb,and the heteroatom Z is selected from the group consisting of Iaelements and Ib elements.